Changeable speed transmissions for bicycles have been proposed and used for many years. These have included various rear wheel hub transmissions, which typically achieved two or three specified speed reductions, as well as derailleur systems, which use the driving chain as a force transmitting element between selectable rear and/or front sprockets.
Both prior systems have readily-identifiable drawbacks. The limited space available within a rear wheel hub of a bicycle places severe limits on the amount of mechanism that can be included within it, and thereby prevents one from designing such a transmission with many speed changes. Derailleurs, while mechanically simple and externally accessible for adjustment and repair, exert side loading forces on driving chains designed for power transmission in a straight line. They also are subject to the frequent need for adjustment due to wear on both the chain and sprockets. The entire derailleur system is exposed to the elements and requires frequent cleaning and lubrication.
The present invention was developed in an effort to provide a continuously variable transmission within the conventional frame components of a bicycle. It is preferably located within the bottom bracket shell of the bicycle frame, but its components can be divided between that location and the interior of the rear wheel hub. In addition, the transmission itself is not limited to bicycle applications, but can be applied to other driving combinations where continuously variable speed changes are desired.
The present invention utilizes pivoting vanes for continuously modifying rotational speed between coaxial driving and driven rotational elements. Prior attempts to design similar transmissions have resulted in detectable speed variations during each revolution of the equipment. The present equipment smooths the speed variations and provides a practical solution to many of the limitations previously encountered.